Hyperthyroidism - 8/15/2012

This week has so far been pretty heavy on quality
Endocrine learning, and today was no exception. Chief of Service with Dr. Surks today was dedicated to hyperthyroidism, specifically around a patient admitted with
3-4 months of weight loss, increased appetite who was ultimately diagnosed with
Grave’s Disease. So let’s talk about when the thyroid works too much and breaks
duty hour regulations…

Hyperthyroidism is not a terribly common illness
– it has a prevalence of 1.3%, and is much more common in women as compared to
men (about a 5:1 ratio). The prevalence increases to 4-5% in elderly women.

Of the potential etiologies, Grave’s Disease is
by far the most common (pre-test probabilities people…), and represents 50-80%
of presenting cases. There are
several other much less common causes – on the attached 2008 review article,
Table 2 provides a nice review.

Can we use history and physical to accurately
diagnose hyperthyroidism? Absolutely. Eyelid retraction (+LR of 30), lid lag
(+LR of ~20), and fine finger tremor (+LR ~10) are particular powerful POSITIVE
signs. The absence of a pulse > 90 (-LR of 0.2), an enlarged thyroid (-LR of
0.1), and fine finger tremor (-LR of 0.3) are particularly powerful NEGATIVE
signs.

The Wayne Index (attached), which is like 50
years old, is also a very handy tool. Scoring ≥ 20 points has a +LR of around
20, and scoring < 11 points has a +LR of 0.04 – both also very powerful…

Geriatric hyperthyroidism is a bit of a
different disease, and the above clinical tools may not be as useful. In
particular, they have less tachycardia and goiter than younger patients. More
specifically, in one study, up to one-third of elderly patients with
hyperthyroidism had a Wayne Index score of < 11.

Once we diagnose hyperthyroidism via the above
clinical tools and then subsequent thyroid function studies, it is then
important to determine the etiology. This is where a radioactive iodine uptake
scan comes in:

HIGH uptake
scans indicate synthesis of hormone, and are consistent with Grave’s (diffuse
uptake), and toxic adenoma/multinodular goiter (more localized uptake); in
Grave’s disease, anti-thyroglobulin antibodies are also helpful, if positive.

LOW uptake
scans represent destruction of thyroid tissue with release of hormone, and
consistent with thyroiditis (as Dr. Surks mentioned, probably more common than
we think, as the majority is probably subclinical), amiodarone toxicity,
radiation, etc. Of note, iodine loads for contrast procedures may lead to a
falsely negative scan as well…

So what do we do for these patients? Well, it
differs a bit dependent on the etiology, but let’s focus on Grave’s:

Methimazole, the most commonly used anti-thyroid
medication, is effective in making patients euthyroid after 4-8 weeks of
therapy. Though 20-30% of patients in the U.S obtain long-term remission, the
majority relapse, and ultimately require definitive therapy…which brings us to…

Radioactive Iodine…there are two approaches to RAI – treat with enough iodine to make a patient
euthyroid, or aim to destroy the gland completely, ultimately leading to a
hypothyroid state. Though the former avoids long-term thyroxine
supplementation, most of these patients will require repeated doses due to
persistent subclinical or overt hyperthyroidism. Even in patients who get an
ablative dose, 10-20% may need subsequent dosing (usually in patients with more
severe disease).

Surgery is also an option for patients with
Grave’s, but generally reserved for patients with more unique situations –
large goiters, patients who wish for definitive therapy, patients who do want
RAI, and most importantly, patients who have a coexisting suspicious nodule.

A quick blurb on an important hyperthyroid related
inpatient issue – thyroid storm (review article attached). Though relatively
rare, it is life-threatening, and carries a significant mortality (10-15%)

The most common etiology is again, Grave’s
Disease, but usually there is some associated precipitating, stress-inducing
factor – surgery, infection, trauma, giving birth are some common scenarios.

Diagnosis is clinical, and Table 1 of the
attached review article provides one of the more commonly used diagnostic
criteria scheme. Generally speaking, the symptoms are mainly a marked
exacerbation of general hyperthyroid symptoms.